<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .a {
            height: 500px;
            display: table;
            width: 100%;
            /* 固定宽高 */
            table-layout: fixed;
        }

        .a1 {
            /* 表格写的宽高可以被内容撑开 */
            width: 100px;
        }

        .a1,
        .a2 {

            display: table-cell;
            border: 1px solid #000;
        }
    </style>
</head>

<body>

    <div class="a">
        <div class="a1">1111111111111111111111111111111111111111111111111111111111</div>
        <div class="a2"></div>
    </div>

</body>

</html>